Method and apparatus for automatically adjusting the bandwidth of an electronic amplifier

ABSTRACT

A method and apparatus are provided for using an automatic BW adjustment circuit to automatically adjust the bandwidth of an electronic amplifier based on the amplitude of a signal that is output from a variable gain amplifier or of one or more variable gain stages that follow the amplifier. By automatically adjusting the bandwidth of the electronic amplifier based on the amplitude of the signal, bandwidth enhancement can be provided while also preventing, or at least reducing, peaking of the frequency response of the electronic amplifier.

TECHNICAL FIELD OF THE INVENTION

The invention relates to electronic amplifiers, and more particularly,to a method and apparatus for automatically adjusting the bandwidth ofan electronic amplifier based on the gain of an output signal of theamplifier or of one or more gain stages that follow the amplifier.

BACKGROUND OF THE INVENTION

Electronic amplifiers come in a variety of configurations and types. Forexample, the term “electronic amplifier” applies to a current-to-voltage(I-V) amplifier, a voltage-to-voltage (V-V) amplifier, avoltage-to-current (V-I) amplifier, and a current-to-current (I-I)amplifier. Electronic amplifiers receive an electronic input signal andproduce an electronic output signal that corresponds to the input signalmultiplied by a gain factor, which is some non-zero positive or negativevalue.

One well-known type of I-V amplifier is a transimpedance amplifier(TIA). TIAs are often used in optical transceiver modules. In opticaltransceiver modules, a photodiode receives an optical signal passing outof the end of an optical fiber and produces an electrical currentsignal, which is then input to a TIA. The TIA then converts theelectrical current signal into an electrical voltage signal, which isthen output from the TIA. Other electrical circuitry downstream of theTIA processes the electrical voltage signal to recover the data bits.

Optical transceiver modules are typically required to be robust in termsof jitter performance and power consumption. In order to improve jitterperformance in optical transceiver modules, it is known to includebandwidth (BW)-enhancement circuitry that increases the BW of the TIA.BW-enhancement circuitry used for this purpose adds a zero to thefrequency response of the TIA to compensate for the effect of a polethat exists in the frequency response of the TIA. This BW-enhancementcircuitry may take many forms, but one well known example is aresistor-capacitor (RC) shunt circuit. The disadvantage of this type ofBW-enhancement circuitry is that it often results in “peaking” of thefrequency response of the TIA, i.e., an overshooting of the gain of thefrequency response. In high-speed optical transceiver modules thatutilize adaptive equalizers, peaking should be minimized or preventedbecause the input signal to the equalizer must generally be linear inorder for the equalizer to properly perform equalization.

An important characteristic of an electronic amplifier is the gain-BW(GBW) product, which is the product of the BW of the amplifier and thegain at which the BW is measured. The GBW product for an amplifier isgenerally constant over the operating range of the amplifier whenamplifier biasing is not changed. Thus, an increase in the gain of theamplifier is usually accompanied by a decrease in BW, and vice versa.One way to reduce peaking is to reduce the BW of the amplifier. However,simply reducing the BW of the amplifier is undesirable in many cases andis counter to the goal of providing BW enhancement.

Accordingly, a need exists for way to provide BW enhancement in anelectronic amplifier while also preventing, or at least reducing,peaking of the frequency response of the amplifier.

SUMMARY OF THE INVENTION

The invention is directed to an apparatus and a method for automaticallyadjusting the BW of an electronic amplifier. The apparatus comprises anelectronic amplifier having a BW that is adjustable, an amplitudedetector circuit having an input that is electrically coupled to anoutput of the electronic amplifier, and an automatic BW adjustmentcircuit having an input that is electrically coupled to an output of theamplitude detector circuit and having an output that is electricallycoupled to circuitry of the electronic amplifier. The electronicamplifier receives a first input signal and produces a first outputsignal that is an amplified version of the first input signal. Theamplitude detector circuit detects the amplitude of the first outputsignal and produces an amplitude detection signal indicative of theamplitude of the first output signal. The automatic BW adjustmentcircuit produces a BW adjustment signal that is based on the amplitudedetection signal. The BW adjustment signal that is output by theautomatic BW adjustment circuit is received by circuitry of theelectronic amplifier. The electronic amplifier adjusts its BW based onthe BW adjustment signal.

The method is as follows. The electronic amplifier receives a firstinput signal at its input and outputs a first output signal at itsoutput corresponding to an amplified version of the first input signal.The electronic amplifier amplifies the first input signal by a non-zerogain value to produce the amplified version of the first input signal.The amplitude detector circuit detects the amplitude of the first outputsignal and produces an amplitude detection signal indicative of theamplitude of the first output signal. The automatic BW adjustmentcircuit receives the amplitude detection signal at its input andproduces a BW adjustment signal that is based on the amplitude detectionsignal, which is then output from the automatic BW adjustment circuitand received by circuitry of the electronic amplifier. The electronicamplifier adjusts its BW based on the BW adjustment signal.

These and other features and advantages of the invention will becomeapparent from the following description, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of the apparatus for performingautomatic BW adjustment in an amplifier in accordance with anillustrative embodiment.

FIG. 2 illustrates a block diagram of the apparatus for performingautomatic BW adjustment in an amplifier in accordance with anotherillustrative embodiment.

FIG. 3 illustrates an example of a schematic diagram of BW-enhancementcircuitry that may be incorporated into the amplifier shown in FIG. 2and controlled to perform automatic BW adjustment.

FIG. 4 illustrates an example of a schematic diagram of BW-adjustmentcircuitry that may be incorporated into the amplifier shown in FIG. 2and controlled to perform automatic BW adjustment.

FIG. 5 illustrates an example of a schematic diagram of BW-enhancementcircuitry that may be employed in the amplifier shown in FIGS. 1 and 2and controlled to perform automatic BW adjustment.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

In accordance with embodiments of the invention, the BW of an electronicamplifier is automatically adjusted by an automatic BW-adjustmentcircuit based on the amplitude of a signal that is output from theamplifier or from one or more gain stages that follow the amplifier. Inthis way, BW enhancement can be provided while also preventing, or atleast reducing, peaking.

The apparatus includes an electronic amplifier, an amplitude detectorcircuit, and an automatic BW adjustment circuit. An output of theelectronic amplifier is electrically coupled to an input of theamplitude detector circuit, although one or more gain stages may beinterposed between the output of the electronic amplifier and the inputof the amplitude detector circuit. An output of the amplitude detectorcircuit is electrically coupled to an input of the automatic BWadjustment circuit. An output of the automatic BW adjustment circuit iselectrically coupled to a node of the amplifier. The amplitude detectorcircuit receives at least a portion of the signal that is output fromthe amplifier or from one or more gain stages that follow the amplifier.The amplitude detector circuit then outputs a signal indicative of theamplitude of the signal. The automatic BW adjustment circuit receivesthe signal output from the amplitude detector circuit and produces aBW-adjustment signal at an output thereof, which is then applied tocircuitry of the amplifier. The BW-adjustment signal causes the BW ofthe amplifier to be adjusted based on the amplitude detected by theamplitude detector circuit.

Typically, but not necessarily, when the amplitude of the signaldetected by the amplitude detector circuit decreases, the BW-adjustmentsignal that is output from the automatic BW adjustment circuit willcause the BW of the amplifier to be reduced, and vice versa. A fewillustrative, or exemplary, embodiments will now be described withreference to FIGS. 1-5.

FIG. 1 illustrates a block diagram of the apparatus 1 for performingautomatic BW adjustment in an amplifier in accordance with anillustrative embodiment. The apparatus 1 includes an electronicamplifier 2, an amplitude detector circuit 4, and an automatic BWadjustment circuit 10. The electronic amplifier 2 may be an I-Vamplifier, a V-I amplifier, a V-V amplifier, or an I-I amplifier. Theamplifier 2 receives an electrical current or voltage signal 11 at aninput thereof and produces an electrical current or voltage signal 12 atan output thereof. One or more gain stages (not shown) may follow theamplifier 2 to provide further amplification of the output signal 12, aswill be described below with reference to FIG. 2. A portion of theelectrical signal 12 is then received at an input of the amplitudedetector circuit 4, which then outputs an electrical signal 14indicative of the amplitude of the signal 12. The automatic BWadjustment circuit 10 receives the signal 14 and processes the signal 14to produces a BW adjustment signal 20. The BW adjustment signal 20 isthen fed back to the amplifier 2. The amplifier 2 then adjusts its BWbased on the BW adjustment signal 20.

The amplifier 2 typically includes BW-enhancement circuitry (not shown)for increasing the BW of the amplifier 2, as will be described below indetail with reference to FIGS. 3 and 5. In accordance with illustrativeembodiments described herein, the BW-adjustment signal 20 that is outputfrom the automatic BW adjustment circuit 10 is applied to theBW-enhancement circuitry of the amplifier 2 to cause the BW of theamplifier 2 to be adjusted by the BW-enhancement circuitry. As indicatedabove, BW-enhancement circuitry is well known and often includes an RCcircuit that adds a zero to the frequency response of the amplifier tocompensate for the effect of a pole that exists in the frequencyresponse of the amplifier. In accordance with illustrative embodimentsdescribed herein, the BW-adjustment signal 20 causes the value of thecapacitance of the RC circuit to be varied in a way that adjusts thelocation of the zero in the frequency response to vary the effect thatthe zero has on the pole. In this way, the automatic BW adjustmentcircuit 10 adjusts the BW of the amplifier 2 based on the amplitude ofthe signal 12.

FIG. 2 illustrates a more detailed block diagram of the apparatus 1shown in FIG. 1 in accordance with an illustrative embodiment. Inaccordance with this illustrative embodiment, the amplifier 2 is a TIA,which, as stated above, is an I-V amplifier. The TIA 2 has first andsecond amplifier stages 2 a and 2 b, respectively, and first and secondfeedback loops 2 c and 2 d, respectively. The first and second feedbackloops 2 c and 2 d have first and second resistors 2 e and 2 f,respectively. The first resistor 2 e provides the I-V conversion of theinput signal 11. The second resistor 2 f is a replica of the firstresistor 2 e and is provided to enable pseudo-random differentialoperation of the amplifier 2. The input electrical current signal 11 isreceived at an input of the first amplifier stage 2 a and convertedthereby into a first voltage signal, V1, which is then input to thesecond amplifier stage 2 b. The second amplifier stage 2 b is a voltagefollower that produces the electrical voltage signal 12, which is thenoutput from the TIA 2.

In accordance with this illustrative embodiment, a gain circuit 3follows the electronic amplifier 2 and is interposed between the outputof the electronic amplifier 2 and the input of the amplitude detectorcircuit 4. The gain circuit 3 comprises first and second variable-gainamplifier stages 3 a and 3 b that amplify the signal 12 to produceamplified voltage signal 13. The amplified voltage signal 13 may beprocessed by additional circuitry (not shown) downstream of theapparatus, such as, for example, data bit recovery circuitry.

In accordance with this illustrative embodiment, the amplitude detectorcircuitry 4 is part of a known AGC 4 a, which varies the gain of theamplifier stages 3 a and 3 b in a known manner based on the detectedamplitude of the signal 13 output from the gain circuitry 3. Thus, thesignal that is output from the AGC 4 a and used to control the gains ofthe amplifier stages 3 a and 3 b is also used by the automatic BWadjustment circuit 10 to produce the BW-adjustment signal 20. Thus, inaccordance with this illustrative embodiment, the BW of the amplifier 2is adjusted based on the output of the AGC 4 a.

The automatic BW adjustment circuit 10 may be any function generatorthat is suitable for receiving the signal 14 output from the AGC 4 a andproducing the BW-adjustment signal 20. The function generator may simplybe a linear function generator that multiplies the signal 14 by a scalarvalue or it may be a nonlinear function generator that multiplies thesignal 14 by some nonlinear function (e.g., parabolic), or somecombination of the two types of functions. The invention is not limitedto any particular type or configuration for the function generator.Also, the automatic BW adjustment circuit 10 may include components orelements in addition to the function generator.

The amplifier 31 shown in FIG. 2 represents an inverter driver thatinverts the signal 13 output from the amplifier stage 3 b. The resistors32 and 33 represent a load that is driven by the amplifier 31. Theamplifier 31 and resistors 32 and 33 are optional and are shown merelyfor the purpose of demonstrating circuitry downstream of the TIA 2 in anoptical receiver or transceiver module.

FIG. 3 illustrates a schematic diagram of an exemplary circuitconfiguration of BW-enhancement circuitry 40 of the type that is oftenused in TIAs. However, in accordance with this embodiment, theBW-enhancement circuitry 40 is configured to have the BW adjustmentsignal 20 applied to a node thereof in order to perform BW adjustment inthe amplifier 2 in accordance with the invention. Thus, theBW-enhancement circuitry 40 is configured to perform BW adjustment inaccordance with the invention.

The BW-enhancement circuitry 40 is typically part of the first amplifierstage 2 a. The BW-enhancement circuitry 40 is a common emitterconfiguration comprising a transistor 41, an RC circuit 42 comprising aresistor 42 a in parallel with two adjustable capacitors, or varactors,42 b and 42 c, a load resistor 43, and a voltage supply, V_(CC), 44. Theinput current signal 11 is applied to the base of the transistor 41. TheRC circuit 42 is connected to the emitter of the transistor 41. The loadresistor 43 is connected between the collector of the transistor 41 andthe voltage supply 44.

The BW-enhancement circuitry 40 operates as follows. The signal V_(CT)corresponds to the BW-adjustment signal 20 that is output from theautomatic BW adjustment circuit 10. The signal 20 is applied to a node45 that is in between the adjustable capacitors 42 b and 42 c. The valueof the signal 20 causes the capacitance values of the adjustablecapacitors 42 b and 42 c to be adjusted by particular amounts, whichcauses the BW of the amplifier 2 to adjust. In essence, the adjustmentin the capacitance values causes the location of the zero in thefrequency response of the amplifier 2 to move such that the manner inwhich the zero compensates for the effect of the pole in the frequencyresponse changes.

FIG. 4 illustrates a schematic diagram of an exemplary circuitconfiguration of BW-adjustment circuitry 50 that may be incorporatedinto the first stage 2 a of the amplifier 2 shown in FIG. 2 to performBW adjustment. The BW-adjustment circuitry 50 may be employed in theamplifier 2 when the aforementioned BW-enhancement circuitry (e.g., FIG.3) is not employed in the amplifier 2. In contrast to the circuitconfiguration shown in FIG. 3, which adds a zero to compensate for theeffects of a pole in the frequency response of the amplifier 2, thecircuit configuration shown in FIG. 4 adds a pole to the frequencyresponse of the amplifier 2. As will be described below in more detail,the BW-adjustment signal 20 is applied to a node of the BW-adjustmentcircuitry 50 to cause the frequency of the pole to be varied, therebycausing the BW of the amplifier to be adjusted.

The BW-adjustment circuitry 50 comprises a transistor 51, an RC circuit52 comprising a resistor 52 a in parallel with two adjustablecapacitors, or varactors, 52 b and 52 c, a load resistor 53, and avoltage supply, V_(CC), 54. The input current signal 11 is applied tothe emitter of the transistor 51. A bias voltage, V_(b), is applied tothe base of the transistor 51. The RC circuit 52 is connected to thecollector of the transistor 51. The load resistor 53 is connectedbetween the emitter of the transistor 51 and ground. The BW-adjustmentcircuitry 50 operates as follows. The signal V_(CT), which correspondsto the BW-adjustment signal 20, is applied to a node 55 that is inbetween the adjustable capacitors 52 b and 52 c. The value of the signal20 causes the capacitance values of the adjustable capacitors 52 b and52 c to be adjusted, which causes the BW of the amplifier 2 to adjust.As indicated above, the adjustment in the capacitance values causes thelocation of the pole in the frequency response of the amplifier 2 tomove, which changes the frequency of the pole, thereby changing the BWof the amplifier 2.

FIG. 5 illustrates yet another exemplary circuit configuration ofBW-enhancement circuitry 60 that may be employed in the amplifier 2 foradjusting the BW of the amplifier based on the BW-adjustment signal 20.The BW-enhancement circuitry 60 is typically employed in the amplifier2, which, in accordance with this embodiment, is the single-stageamplifier shown in FIG. 5. The BW-enhancement circuitry 60 includesfirst, second and third resistors 61, 62 and 63, respectively, atransistor 64, and first and second adjustable capacitors, or varactors,65 and 66, respectively. The resistors 61 and 62 and the adjustablecapacitors 65 and 66 together form a T-shaped RC network 67 thatprovides a zero in the frequency response of the amplifier. The inputsignal 11, which in this case is a current signal, is electricallycoupled to the base of transistor 64 through the T-shaped RC network 67.The collector of the transistor 64 is connected as a feedback loop backto the input terminal 68. The output terminal 69 outputs the voltagesignal V_(OUT), which corresponds to signal 12. The resistors 61 and 62perform the current-to-voltage conversion.

The BW-enhancement circuitry 60 operates as follows. The signal V_(CT)corresponds to the BW-adjustment signal 20 that is output from theautomatic BW adjustment circuit 10. The signal 20 is applied to a nodethat is in between the adjustable capacitors 65 and 66. The value of thesignal 20 causes the capacitance values of the adjustable capacitors 65and 66 to be adjusted by particular amounts, which causes the BW of theamplifier 2 to adjust. In essence, the adjustment in the capacitancevalues causes the location of the zero in the frequency response of theamplifier 2 to move such that the manner in which the zero compensatesfor the effect of the pole in the frequency response changes.

It should be noted that the BW-enhancement or adjustment circuitry thatis employed in the amplifier 2 is not limited to the configurationsshown in FIGS. 3-5. The configurations shown in FIGS. 3-5 are merelyexamples of BW-enhancement or adjustment circuitry that may be used forthis purpose, as will be understood by persons skilled in the art inview of the description provided herein. One of the advantages of usingBW-enhancement circuitry of the type shown in FIG. 3 is that TIAs areoften equipped with such circuitry, which obviates the need to provideadditional circuitry in the amplifier for the purpose of adjusting theBW of the amplifier 2. However, as will be understood by persons skilledin the art, in view of the discussion provided herein, BW adjustment maybe performed in other ways using other circuit configurations.

It should be noted that the invention has been described with respect toillustrative embodiments for the purpose of describing the principlesand concepts of the invention. The invention is not limited to theseembodiments, as will be understood by persons of skill in the art inview of the description provided herein. For example, the invention isnot limited to the circuit configurations shown in FIGS. 2-5. As will beunderstood by those skilled in the art in view of the description beingprovided herein, many modifications may be made to the embodimentsdescribed herein while still achieving the goals of the invention, andall such modifications are within the scope of the invention.

What is claimed is:
 1. An apparatus for automatically adjusting thebandwidth (BW) of an electronic amplifier, the apparatus comprising: anelectronic amplifier having an input for receiving a first input signaland an output for outputting a first output signal corresponding to anamplified version of the first input signal, the electronic amplifieramplifying the first input signal by a non-zero gain value to producethe amplified version of the first input signal, the electronicamplifier having a BW that is adjustable, the electronic amplifierincluding BW-enhancement circuitry capable of enhancing the BW of theelectronic amplifier, the BW-enhancement circuitry includes at least oneresistor and at least one variable capacitor; an amplitude detectorcircuit having an input and an output, the input of the amplitudedetector circuit being electrically coupled to the output of theelectronic amplifier for receiving at least a portion of the firstoutput signal, the amplitude detector circuit detecting an amplitude ofthe first output signal and producing an amplitude detection signalindicative of an amplitude of the first output signal; and an automaticBW adjustment circuit having an input that is electrically coupled tothe output of the amplitude detector circuit for receiving the amplitudedetection signal, the automatic BW adjustment circuit being configuredto produce a BW adjustment signal that is based on the amplitudedetection signal, the automatic BW adjustment circuit having an outputfor outputting the BW adjustment signal, the output of the automatic BWadjustment circuit being electrically coupled to the electronicamplifier such that the BW adjustment signal is applied to a node of theBW-enhancement circuitry to cause at least one capacitance value of saidat least one variable capacitor to be varied, and wherein the variationin the capacitance value causes the BW of the electronic amplifier to beadjusted; and a gain circuit having an input that is electricallycoupled to the output of the electronic amplifier for receiving thefirst output signal and having an output that is electrically coupled tothe input of the amplitude detector circuit, the gain circuit comprisingat least one adjustable gain stage that receives the first output signaland amplifies the first output signal to produce an amplified firstoutput signal, the gain circuit amplifying the first output signal by anon-zero gain value to produce the amplified first output signal, andwherein the amplitude detection signal is indicative of an amplitude ofthe amplified first output signal.
 2. The apparatus of claim 1, whereinthe amplitude detector circuit is part of an automatic gain control(AGC) circuit, and wherein the AGC circuit adjusts a gain of said atleast one gain stage of the gain circuit based on the amplitude of theamplified first output signal.
 3. The apparatus of claim 2, wherein theelectronic amplifier is a current-to-voltage (I-V) electronic amplifiersuch that the first input signal is an electrical current signal and thefirst output signal is an electrical voltage signal.
 4. The apparatus ofclaim 3, wherein the electronic amplifier is a transimpedance amplifier,and wherein the apparatus is part of an optical receiver.
 5. Theapparatus of claim 1, wherein the electronic amplifier is acurrent-to-current (I-I) electronic amplifier such that the first inputsignal is an electrical current signal and the first output signal is anelectrical current signal.
 6. The apparatus of claim 1, wherein theelectronic amplifier is a voltage-to-voltage (V-V) electronic amplifiersuch that the first input signal is an electrical voltage signal and thefirst output signal is an electrical voltage signal.
 7. The apparatus ofclaim 1, wherein the electronic amplifier is a voltage-to-current (V-I)electronic amplifier such that the first input signal is an electricalvoltage signal and the first output signal is an electrical currentsignal.
 8. The apparatus of claim 1, wherein said at least one resistoris in parallel with said at least one variable capacitor.
 9. Anapparatus for automatically adjusting the bandwidth (BW) of anelectronic amplifier, the apparatus comprising: an electronic amplifierhaving an input for receiving a first input signal and an output foroutputting a first output signal corresponding to an amplified versionof the first input signal, the electronic amplifier amplifying the firstinput signal by a non-zero gain value to produce the amplified versionof the first input signal, the electronic amplifier having a BW that isadjustable, the electronic amplifier including BW-enhancement circuitrycapable of enhancing the BW of the electronic amplifier, theBW-enhancement circuitry including at least at least two variablecapacitors connected in series with each other and in parallel with saidat least one resistor; an amplitude detector circuit having an input andan output, the input of the amplitude detector circuit beingelectrically coupled to the output of the electronic amplifier forreceiving at least a portion of the first output signal, the amplitudedetector circuit detecting an amplitude of the first output signal andproducing an amplitude detection signal indicative of an amplitude ofthe first output signal; and an automatic BW adjustment circuit havingan input that is electrically coupled to the output of the amplitudedetector circuit for receiving the amplitude detection signal, theautomatic BW adjustment circuit being configured to produce a BWadjustment signal that is based on the amplitude detection signal, theautomatic BW adjustment circuit having an output for outputting the BWadjustment signal, the output of the automatic BW adjustment circuitbeing electrically coupled to the electronic amplifier such that the BWadjustment signal is applied to a node of the BW-enhancement circuitrythat is in between the two capacitors to cause capacitance values ofsaid at least two variable capacitors to be varied, and wherein thevariation in the capacitance values causes the BW of the electronicamplifier to be adjusted.
 10. The apparatus of claim 9, wherein theelectronic amplifier is a current-to-current (I-I) electronic amplifiersuch that the first input signal is an electrical current signal and thefirst output signal is an electrical current signal.
 11. The apparatusof claim 9, wherein the electronic amplifier is a voltage-to-voltage(V-V) electronic amplifier such that the first input signal is anelectrical voltage signal and the first output signal is an electricalvoltage signal.
 12. The apparatus of claim 9, wherein the electronicamplifier is a voltage-to-current (V-I) electronic amplifier such thatthe first input signal is an electrical voltage signal and the firstoutput signal is an electrical current signal.
 13. The apparatus ofclaim 9, wherein the electronic amplifier is a current-to-voltage (I-V)electronic amplifier such that the first input signal is an electricalcurrent signal and the first output signal is an electrical voltagesignal.
 14. The apparatus of claim 13, wherein the electronic amplifieris a transimpedance amplifier, and wherein the apparatus is part of anoptical receiver.
 15. A method for automatically adjusting the bandwidth(BW) of an electronic amplifier, the method comprising: in an electronicamplifier, receiving a first input signal at an input of the electronicamplifier and outputting a first output signal at an output of theelectronic amplifier, the first output signal corresponding to anamplified version of the first input signal, the electronic amplifieramplifying the first input signal by a non-zero gain value to producethe amplified version of the first input signal, the electronicamplifier having a BW that is adjustable, the electronic amplifierincluding BW-enhancement circuitry capable of enhancing the BW of theelectronic amplifier, the BW-enhancement circuitry including at leastone resistor and at least one variable capacitor; in an amplitudedetector circuit having an input that is electrically coupled to theoutput of the electronic amplifier, detecting an amplitude of the firstoutput signal, producing an amplitude detection signal indicative of anamplitude of the first output signal, and outputting the amplitudedetection signal at an output of the amplitude detector circuit; in anautomatic BW adjustment circuit having an input that is electricallycoupled to an output of the amplitude detector circuit, receiving theamplitude detection signal, producing a BW adjustment signal that isbased on the amplitude detection signal, and outputting the BWadjustment signal at an output of the automatic BW adjustment circuit,the output of the automatic BW adjustment circuit being electricallycoupled to the electronic amplifier; and in the electronic amplifier,receiving the BW adjustment signal at a node of the BW-enhancementcircuitry, wherein receipt of the BW adjustment signal at the nodecauses at least one capacitance value of said at least one variablecapacitor to be varied, and wherein the variation in the capacitancevalue causes the BW of the electronic amplifier to be adjusted; and in again circuit having an input that is electrically coupled to the outputof the electronic amplifier and having an output that is electricallycoupled to the input of the amplitude detector circuit, receiving thefirst output signal and outputting an amplified first output signal atan output of the gain circuit, the gain circuit comprising at least oneadjustable gain stage that receives the first output signal andamplifies the first output signal by a non-zero gain value to producethe amplified first output signal, and wherein the amplitude detectionsignal is indicative of an amplitude of the amplified first outputsignal.
 16. The method of claim 15, wherein the amplitude detectorcircuit is part of an automatic gain control (AGC) circuit, and whereinthe AGC circuit adjusts a gain of said at least one gain stage of thegain circuit based on the amplitude of the amplified first outputsignal.
 17. The method of claim 16, wherein the electronic amplifier isa current-to-voltage (I-V) electronic amplifier such that the firstinput signal is an electrical current signal and the first output signalis an electrical voltage signal.
 18. The method of claim 17, wherein theelectronic amplifier is a transimpedance amplifier, and wherein theapparatus is part of an optical receiver.
 19. The method of claim 15,wherein the electronic amplifier is a current-to-current (I-I)electronic amplifier such that the first input signal is an electricalcurrent signal and the first output signal is an electrical currentsignal.
 20. The method of claim 15, wherein the electronic amplifier isa voltage-to-voltage (V-V) electronic amplifier such that the firstinput signal is an electrical voltage signal and the first output signalis an electrical voltage signal.
 21. The method of claim 15, wherein theelectronic amplifier is a voltage-to-current (V-I) electronic amplifiersuch that the first input signal is an electrical voltage signal and thefirst output signal is an electrical current signal.
 22. The method ofclaim 15, wherein said at least one resistor is in parallel with said atleast one variable capacitor.
 23. A method for automatically adjustingthe bandwidth (BW) of an electronic amplifier, the method comprising: inan electronic amplifier, receiving a first input signal at an input ofthe electronic amplifier and outputting a first output signal at anoutput of the electronic amplifier, the first output signalcorresponding to an amplified version of the first input signal, theelectronic amplifier amplifying the first input signal by a non-zerogain value to produce the amplified version of the first input signal,the electronic amplifier having a BW that is adjustable, the electronicamplifier including BW-enhancement circuitry capable of enhancing the BWof the electronic amplifier, the BW-enhancement circuitry including atleast two variable capacitors connected in series with each other and inparallel with said at least one resistor; in an amplitude detectorcircuit having an input that is electrically coupled to the output ofthe electronic amplifier, detecting an amplitude of the first outputsignal, producing an amplitude detection signal indicative of anamplitude of the first output signal, and outputting the amplitudedetection signal at an output of the amplitude detector circuit; in anautomatic BW adjustment circuit having an input that is electricallycoupled to an output of the amplitude detector circuit, receiving theamplitude detection signal, producing a BW adjustment signal that isbased on the amplitude detection signal, and outputting the BWadjustment signal at an output of the automatic BW adjustment circuit,the output of the automatic BW adjustment circuit being electricallycoupled to the electronic amplifier; and in the electronic amplifier,receiving the BW adjustment signal at a node of the BW-enhancementcircuitry that is in between the two capacitors, wherein receipt of theBW adjustment signal at the node causes capacitance values of the twovariable capacitors to be varied, and wherein the variation in thecapacitance values causes the BW of the electronic amplifier to beadjusted.
 24. The method of claim 23, wherein the amplitude detectorcircuit is part of an automatic gain control (AGC) circuit, and whereinthe AGC circuit adjusts a gain of said at least one gain stage of thegain circuit based on the amplitude of the amplified first outputsignal.
 25. The method of claim 23, wherein the electronic amplifier isa current-to-current (I-I) electronic amplifier such that the firstinput signal is an electrical current signal and the first output signalis an electrical current signal.
 26. The method of claim 23, wherein theelectronic amplifier is a voltage-to-voltage (V-V) electronic amplifiersuch that the first input signal is an electrical voltage signal and thefirst output signal is an electrical voltage signal.
 27. The method ofclaim 23, wherein the electronic amplifier is a voltage-to-current (V-I)electronic amplifier such that the first input signal is an electricalvoltage signal and the first output signal is an electrical currentsignal.
 28. The method of claim 23, wherein the electronic amplifier isa current-to-voltage (I-V) electronic amplifier such that the firstinput signal is an electrical current signal and the first output signalis an electrical voltage signal.
 29. The method of claim 28, wherein theelectronic amplifier is a transimpedance amplifier, and wherein theapparatus is part of an optical receiver.